Autostereoscopic 3D image display devices are classified into a type using an optical plate, such as a lenticular lens or parallax barrier, and a type using a line light source array for forming a viewing zone. The 3D image display devices using the parallax barrier, the lenticular lens, and the line light source array for forming the viewing zone have a crosstalk phenomenon in which a distribution of light and an image of an adjacent viewpoint are partially overlapped with each other according to movement of eyes even in the same viewing zone. Accordingly, it is difficult to implement a natural 3D image when a viewer moves, thereby causing viewer inconvenience.
FIG. 1 shows a brightness distribution of viewing zones for viewpoints according to horizontal position movement of the conventional autostereoscopic 3D image display device using the parallax barrier at an optimal viewing distance. In FIG. 1, on the assumption that a distance between viewpoints is the same as a distance between a viewer's pupils (about 65 mm), when the viewer at the optimal viewing distance is positioned in front of the 3D image display device, the left eye of the viewer is positioned at a center of a first viewing zone (position A), and the right eye of the viewer is positioned at a center of a second viewing zone (position C), an image in the corresponding viewing zone of each viewpoint becomes dark rapidly as both of the viewer's eyes deviate from the position A and the position C, thereby degrading image quality. Further, a portion of an image disposed in the first viewing zone and a portion of an image disposed in a third viewing zone are simultaneously viewed by the left eye of the viewer even when the left eye is positioned at the center of the second viewing zone, and a portion of a left eye image disposed in the second viewing zone and a portion of an image disposed in a fourth viewing zone are simultaneously viewed by the right eye of the viewer even when the right eye is positioned at the center of the third viewing zone. Accordingly, a certain amount of crosstalk occurs even at the optimal position, and the amount thereof increases when the viewer leaves the optimal position. In particular, when the left eye of the viewer is positioned at a middle position (position B) between the first viewing zone and the second viewing zone, and the right eye of the viewer is positioned at a middle position between the second viewing zone and the third viewing zone, the maximum crosstalk occurs. Further, since the distance between viewpoints is designed to be appropriate for a distance between an average viewer's pupils even when the viewer stops, left and right optimal bright images cannot be viewed in the brightness distribution of the viewing zone of FIG. 1 when a distance between the pupils of a viewer who views a 3D image deviates from the average.
The above problems occur in the conventional autostereoscopic 3D image display device when the viewer views the 3D image at a position near the optimal viewing distance while stopping or moving. In addition, basically, when moving in a depth direction, the viewer cannot view the 3D image well. This will be described with reference to FIGS. 2 to 5.
FIGS. 2 to 5 are diagrams for describing an example of a conventional autostereoscopic 3D image display device using a four-viewpoint parallax barrier. The viewing zones are separated well at the optimal viewing distance as shown in FIG. 1. However, for example, if a viewer leaves an optimal viewing distance (OVD) position in a depth direction and moves toward a position P1 (position at a distance of 0.5 times the OVD), unlike the OVD, a viewing zone for a left eye viewing point and a viewing zone for a right eye viewing point are not separated well and each of the viewing zones overlaps its adjacent viewing zone, and thus the viewer cannot view a 3D image well (see FIG. 4 for the distribution of viewing zones at the position P1). Here, since the viewing zones for respective apertures do not accurately match with each other, adjacent viewing zones are represented as overlapping. FIG. 4 shows a result of simulating all images for the same viewpoint together. A viewing zone for an individual aperture does not expand individually. This phenomenon takes place since position which viewing zone is formed by each aperture varies according to each aperture of 3D display. This result may be seen in FIGS. 7 and 8, which show viewing zone distribution charts for an individual aperture. The individual aperture of the parallax barrier and pixels which view point images are provided defining the viewing zone distribution charts is defined as a 3D pixel line. Alternatively, the 3D pixel line as a unit configuration of 3D viewing zone may be defined by a lenticular lens of one period as parallax separating means and pixels which view point images are provided, or a line source and pixels which view point images are provided in 3D image display. Also, although not shown in FIG. 2, even when the viewer moves to a position at a distance 1.5 times the OVD, as shown in FIG. 5, a viewing zone shape varies for a similar reason to that of FIG. 4 and crosstalk increases. To describe this in more detail with reference to FIG. 4, considering the intersection of boundaries between viewing zones within a dotted line of a position P1 of FIG. 2, when a pupil is positioned at a depth position of the position P1, for example, a position e1, a 3D image may be viewed near the center of the third viewing zone through a central aperture, but a 3D image from a left side aperture is positioned on a boundary between the first viewing zone and the second viewing zone such that the 3D image causes the viewer to experience maximum crosstalk. Also, although a 3D image from a right side aperture is not exactly shown in the drawings, since the 3D image is positioned at a boundary between the fourth viewing zone and a first viewing zone in a sub viewing zone, the 3D image allows a viewer to experience maximum crosstalk and an inverse viewing zone. Accordingly, even when there is one pupil at a center of a viewing zone of any one pixel in consideration of all apertures, there are multiple cases in which one pupil is on a boundary between viewing zones even when the viewing zone closest to the center of the pupil is selected among viewing zones of other apertures, depending on the case. In this case, as described above, the crosstalk is completely or approximately maximized for each aperture. Accordingly, the crosstalk increases on average. This situation occurs even when the distance is far from the OVD. Accordingly, if the viewer is sufficiently far from the OVD, a large amount of crosstalk inevitably occurs at all positions.
Lastly, the conventional autostereoscopic 3D image display device is generally designed such that one viewer may view a 3D image. For a plurality of viewers, the autostereoscopic 3D image display device may allow only viewers positioned at restricted positions, that is, specific positions within the optimal viewing distance, to view a 3D image at their positions.
Accordingly, there is a demand for a autostereoscopic image display device for viewing a natural 3D image even when a plurality of viewers move freely as a solution for the above-described four problems.